Signals from the Past: Cosmic Microwave Background Radiation

The origin of our existence has long been a topic of debate. How did our universe come into existence? Where did the Sun come from? How did humans come to be what we are today? There have been many different theories throughout the years to answer these questions, and while some theories have since been discarded, some are still waiting to be verified. The discovery of cosmic microwave background radiation had implications for the legitimacy one of these theories. This accidental finding in 1964 by two American astronomers was vital for the field of cosmology, and ended up becoming a deciding factor between two competing theories. A discovery of this magnitude has implications that extend to more than just the cosmological and educational field though. The discovery's connection to society, religion, and other aspects of life are vast, and while it unified cosmologists, it could be argued to be a large factor in the division of other areas of thinking and beliefs.

In the beginning

Arno Allan Penzias and Robert Woodrow Wilson were running experiments at the Bell Labs in Holmdel, New Jersey in 1964 when they stumbled upon a discovery that would later win them the Nobel Prize in 1978 [1]. They were using an extremely sensitive 20 foot tall horn antenna to detect radio waves that were being bounced off of echo balloon satellites. Since these radio waves were very faint, they could only measure the waves by eliminating all other interference from their radio receiver. They removed the interference from radio stations and radar, and even were able to suppress the interference from the heat given off by the receiver by cooling it with liquid helium to only 4 degrees Celsius above absolute zero. Even after taking all of these measures to remove interference, they were still picking up a low, steady noise. This mysterious noise was evenly spread out throughout the sky, and it didn’t matter what time of day it was, it was constantly there. The 7.35 centimeter long wavelength radiation that they were detecting was creating a residual noise that was 100 times greater than what they expected to hear. Penzias and Woodrow checked their equipment again to make sure that it wasn’t the source of the noise. They even cleaned out some pigeon nests from their antenna, and the droppings that had accumulated as well. The noise persisted though, and the two astronomers could only conclude that the noise was coming from somewhere outside of our universe. What they didn’t realize is that they had found a piece of evidence that would change the course of modern cosmology by tipping the scales in favor of the big bang theory, and make the steady state theory obsolete.

It just so happens that three astrophysicists at Princeton University named Robert H. Dicke, Jim Peebles, and David Wilkinson were getting ready to search for the radiation that Penzias and Wilson had already accidentally found. Robert H. Dicke was a physicist born in St. Louis, Missouri who made important contributions to cosmology and physics. While he was working on his Brans-Dicke theory, which deals with gravitation and competes with Einstein’s more popular theory of relativity, he started to think more about the early universe. Dicke believed that if the Big Bang had scattered matter that condensed into galaxies, then there should be a considerable amount of left over radiation from that event [1]. So Dicke teamed up with Peebles and they re-derived the prediction of the cosmic microwave background radiation. After they had their prediction, Dicke and Peebles, along with Wilkinson and Peter G. Roll, started building their radiometer to detect this radiation. What they didn’t know was that Penzias and Wilson had already detected it.

A friend of Penzias named Bernard F. Burke informed Penzias of a paper that Jim Peebles had written about possibly finding left over radiation from an explosion at the creation of the universe. When Penzias heard this he realized that he and Wilson had stumbled upon something truly remarkable. Their findings matched up perfectly with what was predicted by Dicke, Peebles, and Wilkinson. Penzias contacted Dicke for a copy of Peebles unpublished paper. After receiving the call from Penzias, Dicke famously quipped, “Boys, we’ve been scooped.” [2]. Penzias read through the paper and then invited Dicke and his colleagues out to the Bell Labs to hear what he and Wilson had found. Dicke and his colleagues concluded that this radiation was in fact a signature of the Big Bang [1]. They all decided that they should publish their results jointly so that they could avoid any potential conflicts. Dicke, Peebles, and Wilkinson submitted a paper discussing the importance of the cosmic background radiation to the Big Bang theory. Then Penzias and Wilson submitted their paper on the existence of residual background noise and claimed a possible explanation could be found in Dicke’s paper.

Cosmic Microwave Background Radiation

At this point an explanation to what cosmic microwave background radiation even is seems necessary. This radiation has multiple names and acronyms to describe it, with most of them including some variation of cosmic, microwave, and background. Examples for its name include CMBR, MBR, and CBR, along with relic radiation being another option. What all of these names stand for though is a thermal radiation that almost uniformly fills the observable universe [2]. When using an extremely sensitive radio telescope, the areas between stars that are normally dark now have a faint glow that isn’t associated with any galaxy or star. This glow is said to be the oldest visible light. This faint glow can be seen in Figure 2 below.

Figure 2, Cosmic Microwave Background Radiation [11]

When looking into the night sky with a telescope, we are actually looking into the past. The universe is so massive that it has been estimated that it may take hours or even thousands to millions of years for light to reach us from other planets or galaxies. For example, when people see Jupiter in the night sky they are looking an hour into the past [3]. Such an ancient source of light is very important for the study of cosmology. It is believed that this radiation is leftover from a time when our universe was smaller and much hotter. As the universe expanded and began to cool off the elementary particles present combined with the radiation and formed what we know of today as stars, planets, and galaxies. Due to the expansion of the universe, the CMBR has also been stretched out and now is in the microwave region of the electromagnetic spectrum. Its wavelength is equal to 1.873 mm, and it has a temperature equal to 2.725 K [2].

The idea of Cosmic Microwave Background Radiation has a relatively short history. It was first predicted to exist by Ralph Alpher and Robert Herman in 1948. They predicted its temperature to be 5 K and then later changed their prediction to be 28 K. Andrew McKellar and Robert Dicke both made predictions on the temperature of the interstellar medium and the temperature of the radiation from cosmic radiation respectively, but they both did not refer to background radiation. A couple more predictions were made throughout the years with resulting values equal to 7 K, 3 K, 6 K, and even 40 K. The first time that CMBR was recognized as a measureable phenomenon though was in a published paper written by two Soviet astrophysics, Andrei G. Doroshkevich and Igor Novikov, in 1964. This was not the only important event in CMBR’s history happening in 1964 though. Roll and Wilkinson, colleagues of Dicke at Princeton, began to build a Dicke radiometer to measure the cosmic microwave background radiation in this year as well. Then 1965 is when Penzias and Wilson performed their famous “scoop” by making their accidental discovery.

Implications for cosmology

Since this discovery was made, there has been a change in the field of cosmology. For example there has been more focus on proving the Big Bang theory. There were two prevailing theories for the origin of our universe before the detection of cosmic microwave background radiation. One theory was the Big Bang theory, which claims that our universe started out extremely dense and hot and then expanded rapidly. The alternative theory was called the steady state theory, which is also referred to as the Infinite Universe theory and continuous creation theory. This theory states that as our universe expands new matter is continuously created, so that it adheres to the perfect cosmological principle. This principle states that the universe is isotropic in space and time and is homogenous. So the steady state theory claims that the universe looks the same everywhere and that it always has and always will look that way. Since the Big Bang theory accurately predicted the existence of this background radiation, the actual detection of CMBR made the Big Bang theory more credible than the Steady State theory, and has since made this rival theory obsolete. This detection was so significant in the decision between the two theories that Stephen Hawking at a lecture at the Centre for mathematical Sciences in Cambridge, UK said, “The final nail in the coffin of the steady state theory came in 1965 with the discovery of a faint background of microwave radiation.” [5].

The discovery itself was obviously important to the field of cosmology, but what the discovery has led to is possibly even more interesting. Like it was stated earlier, this evidence led to the big bang theory becoming the predominate theory in the origin of our universe. This fact increased the focus on the big bang theory and on finding evidence to support it. An example of such evidence found in support of the big bang theory is the abundance of light elements found in the universe. Since helium and hydrogen are so prevalent in the observable universe some cosmologist point to the big bang theory for answering why this is. Another interesting discovery that has come about since the discovery of cosmic background radiation is that the universe appears to not only be expanding, but actually accelerating in its expansion. This is very important to the big bang model because it is possible now to refine the model even more. Some cosmologists believed that the big bang theory actually went through cycles. They believed that the universe started expanding with the big bang, expanded until it reached a point that it stopped expanding and started to collapse in on itself, and then started the process all over again. The discovery that the universe’s expansion is actually accelerating leads to a belief that the universe actually only existed at one time, had one beginning, and is actually expanding until it becomes an extremely dark and cold place. The implications of this new discovery as we understand it now seem to lead to an ending that is vast, somber, and desolate. The discovery of cosmic background radiation led to more than just more discoveries in cosmology though. Its significance is farther reaching than that.

Societal Change

Academia was not the only area that was impacted by this important discovery’s implications. There was also the impact it would have on society. The majority of this impact was on the religious community. There has always been, and probably always will be, at least a small connection between cosmology and religion. So now that there was a single theory that the majority of cosmologists were in agreement with, there became a more unified science community. This unification led to an increase in the teaching of the big bang theory as the origin of our universe, and today it is treated as common knowledge. This unification has also led to much of the work in cosmology today being about extending and refining the big bang theory. This teaching of the universe’s origins has created conflict with the ideals of some religions for years now. What is interesting about this conflict between religion and the big bang theory is that a Catholic priest named George Lemaitre had a large part in formulating this now widely accepted model.

George Lemaitre was a Belgian scientist who started his academic career by getting a bachelor’s degree in mechanical engineering. He would become to be known as more than just an engineer though. He also was a World War I veteran, received a bachelor’s degree in mathematics and philosophy, and a PhD in mathematics before he started to study at Maison Saint Rombaut for his priesthood. He was not done there though. He later went on to do astronomy research at Cambridge and Harvard before getting a PhD in physics from Massachusetts Institute of Technology.This interesting combination of areas of schooling could be how Lemaitre was able to create such an innovative idea such as the primeval atom hypothesis. This hypothesis was the basis for what is now commonly referred to as the big bang theory. He was able to formulate this idea after working through Einstein’s theory of relativity. His calculations showed the universe must be either expanding or contracting, just like what Einstein had found. The difference is that instead of creating a cosmological constant so the calculations corresponded to the steady state theory, like Einstein did, Lemaitre concluded that the universe was expanding. Einstein was a proponent of the steady state theory which blinded his judgment on his own findings. When Lemaitre made his hypothesis public few people took notice at first. Einstein even when so far as to say to Lemaitre, “Your calculations are correct, but your grasp of physics is abominable.” [8]. Einstein and the world would soon see that Lemaitre was in fact correct, and Einstein would later become a supporter and good friend of Lemaitre.

Opponents to the Theory

Not everyone was as supportive as Einstein came to be though. Fred Hoyle, one of the proposers of the steady state theory, made it a point to voice his opposition to the primeval atom hypothesis. He even went as far to “associating the steady state theory with atheism, and, conversely, the big bang theory with religion in general, and theism in particular.” [9]. Some cosmologists complained that the idea of a beginning to our universe let too many religious ideas into the area of science. It is interesting though that many Christian churches are opposed to accepting the big bang theory while an astronomer, who actually coined the named ‘big bang,’ along with other colleges were opposing the same theory due to its religious implications. This may be due to the fact that the theory has changed some over the last 70 years, and has since seemed to cut any sort of ties to religion in general. I believe that this can also be attributed to the notion that science and religion are incompatible. Many scientists work under the belief that it is not possible to let a divine foot in the door. Under this assumption, there will always be conflict between theology and cosmology.

Some religions have tried to be accommodating to the idea of the big bang theory though. Muslim commentators have even stated that the Qur’an refers to the big bang theory, with an example being in Surah 21:30. This verse says, "Do not the unbelievers see that the Heavens and the earth were joined together (as one unit of creation) before we clove them asunder?" [10]. Catholicism has also accepted the big bang theory. Pope Pius XII declared back in 1951 that the big bang theory did not conflict with how creation was viewed by Catholics. Of course there are also other physicists, astronomers, and cosmologists that claim that the big bang theory actually proves that a creator is unnecessary. All of this just adds to the interesting debate between different theologians and cosmologists.

In conclusion

Penzias and Wilson stumbled upon something very significant almost 50 years ago now that would forever change how we try to understand our beginnings. CMBR has created a dominate theory of our universe’s birth, and it has also caused even more controversy between the science and religious communities. While it has created a predominate theory it has almost left even more unanswered questions, and also created more divisions within the big bang model. Is our universe forever expanding or is the expansion just a part of a cycle our universe goes through? Is the universe’s expansion really accelerating? In the end I believe we still haven’t proceeded too far past the original question. How did our universe come into existence?